Hydraulic cranes

Abstract

An improved hydraulic crane comprising at least one lifting cylinder to pivot the crane arm in a vertical plane relative to the crane post. A pressure-fluid line associated with the cylinder is connected to a movement-damping accumulator. In addition, a non-return valve is inserted between the cylinder and the accumulator to allow flow of pressurized liquid in one direction only away from the cylinder. A drainage line is connected to the accumulator, said drainage line incorporating a pressure-limiting valve. Owing to this arrangement, any added loads that arise as a result of sudden, shock-like pressures may be absorbed upon pressure relief in the accumulator without imparting jerky return movements to the crane arms.

What I claim is: 
     
       1. An improved hydraulic crane, comprising a crane post, a lifting arm journalled on said crane post, a lifting cylinder arranged to pivot said lifting arm in a vertical plane, a hydraulic pump, said cylinder connected to said hydraulic pump via a first hydraulic line, a hand valve inserted in said hydraulic line, and a dampening accumulator connected to said first hydraulic line via a second hydraulic line, the improvement comprising a non-return valve inserted in said second hydraulic line connecting said accumulator to said first hydraulic line, said non-return valve allowing flow of pressurized fluid only in the direction away from said lifting cylinder, and a drainage line, said drainage line connected to said accumulator, a pressure-limiting valve inserted in said drainage line and arranged to open in response to a temporary excess pressure in said accumulator for relief of pressure to said drainage line.   
     
     
       2. An improved hydraulic crane as claimed in claim 1, wherein a rocker arm is mounted at the outer end of said lifting arm, a second lifting cylinder arranged to pivot said rocker arm in a vertical plane, the improvement comprising a pressure-fluid line associated with said second cylinder, a third hydraulic line connected with said accumulator, said pressure-fluid line connected to said third hydraulic line, a non-return valve inserted in said third hydraulic line, said non-return valve allowing flow of pressurized fluid only in the direction away from said second lifting cylinder.   
     
     
       3. An improved hydraulic crane as claimed in claim 1, wherein a rocker arm is mounted at the outer end of said lifting arm, a second lifting cylinder arranged to pivot said rocker arm in a vertical plane, the improvement comprising a pressure-fluid line associated with said second cylinder,   a second accumulator, separate from said first accumulator, said second accumulator connected via a third hydraulic line having a non-return valve therein and connected with said pressure-fluid line associated with said second rocker-arm cylinder, and   a drainage line connected to said third hydraulic line between said non-return valve and said second accumulator, a pressure-limiting valve inserted in said drainage line.   
     
     
       4. A hydraulic system which is subject to sudden shock loading pressure comprising in combination: a hydraulic pump;   a hydraulic lift cylinder operatively connected to said pump via a first hydraulic line having a hand valve disposed therein for controlling fluid flow between said pump and said cylinder, said cylinder being subject to sudden shock loading;   an accumulator operatively connected to said first hydraulic line intermediate said hand valve and said cylinder via a second hydraulic line having a non-return valve disposed therein for allowing fluid flow only in a direction away from said cylinder, said accumulator having a drainage line including a pressure-limiting valve whereby said pressure-limiting valve opens in response to any temporary excess pressure in said accumulator due to shock loading of said cylinder and relieves the pressure through said drainage line.   
     
     
       5. A hydraulic crane, comprising in combination: a crane post;   a lifting arm pivotally connected to said crane post;   a hydraulic cylinder operatively connected to said arm and said post for pivoting said arm in a vertical plane, said arm being subject to sudden shock loading;   a hydraulic pump operatively connected to said cylinder via a first hydraulic line having a hand valve therein for controlling fluid flow through said first line between said pump and said cylinder to move said arm;   an accumulator operatively connected to said first line intermediate said hand valve and said cylinder via a second hydraulic line having a non-return valve therein allowing fluid flow only in a direction away from said cylinder, said accumulator having a drainage line with a pressure-limiting valve therein whereby said pressure-limiting valve opens in response to any temporary pressure in said accumulator caused by shock loading on said crane to relieve the excess pressure through said drainage line.   
     
     
       6. A hydraulic system for a loading crane which is subject to sudden shock loading, comprising in combination: a hydraulic pump;   a hydraulic lift cylinder for actuating said crane, operatively connected to said pump via a first hydraulic line having a hand valve therein for controlling fluid flow through said first line between said pump and said cylinder, said cylinder being subject to shock loading;   an accumulator operatively connected to said first hydraulic line intermediate said cylinder and said hand valve via a second hydraulic line having a non-return valve therein for allowing fluid flow therethrough only in a direction away from said cylinder, said accumulator having a drainage line with a pressure-limiting valve therein whereby any temporary excess pressure in said accumulator due to shock loading of said cylinder opens said pressure-limiting valve to relieve the pressure through said drainage line.   
     
     
       7. In a hydraulic crane having a hydraulic piston/cylinder device of predetermined volumetric capacity and accumulator means hydraulically connected to said device for cushioning sudden increases in hydraulic pressure imposed upon said device, said accumulator means having a volumetric cushioning capacity which is at least in the order of said predetermined volumetric capacity of the piston/cylinder device, the improvement which comprises: check valve means hydraulically connected between said accumulator means and said piston/cylinder device for allowing hydraulic fluid flow toward said accumulator means and preventing return hydraulic flow from said accumulator means to said device whereby to trap hydraulic fluid in the accumulator means during a cushioning action thereof; and   means responsive to attainment of a predetermined pressure within said accumulator means for draining trapped hydraulic fluid therefrom.   
     
     
       8. An improved hydraulic crane as claimed in claim 1, wherein a rocker arm is mounted at the outer end of said lifting arm, a second lifting cylinder arranged to pivot said rocker arm in a vertical plane, the improvement comprising a pressure-fluid line associated with said second cylinder, a third hydraulic line connected with said accumulator, said pressure-fluid line connected to said third hydraulic line, a non-return valve inserted in said third hydraulic line, said non-return valve allowing flow of pressurized fluid only in the direction away from said second lifting cylinder   a drainage line connected to said third hydraulic line between said non-return valve and said accumulator, a pressure-limiting valve inserted in said drainage line.